Twenty-two children die after free school lunch

Twenty-two children have died after eating a free lunch feared to contain poisonous chemicals at a school in eastern India, as angry protests erupted over the tragedy.

Thirty more children remain ill in hospital after consuming lunch cooked at a village primary school in the impoverished state of Bihar, state education minister P K Shahi said.

"After 21 deaths, we have just heard that one more child has died while undergoing treatment," the state's health secretary, Vyas Ji, told AFP, as suspicion focused on the possible presence of insecticide in the food.

There were emotional scenes as children, their limbs dangling and heads lolling to one side, were brought to a hospital in the Bihar city of Chhapra.

Twenty of the children, all aged under 10, were buried near the school in the village of Masrakh on Wednesday morning as angry residents armed with poles and sticks took to the streets of Chhapra.

The mob smashed windows of police buses and other vehicles and turned over a police booth in Chhapra, the main city of Saran district where the school is located.

"Hundreds of angry people staged a protest in Saran since late Tuesday night, demanding stern action against government officials responsible for this shocking incident," said district government official S K Mall.

A preliminary investigation has shown the meal may have contained traces of phosphate from insecticide in the vegetables, Sinha from the local government told AFP.

He said doctors were treating victims with atropine, which is effective against organophosphate poisoning.

Media reports quoted villagers as saying the use of contaminated, foul-smelling mustard oil for cooking at the school could also have caused the deaths.

"Investigators are examining midday meal samples and samples of victims' vomit. Only the final report of inquiry will reveal the real cause," Sinha said.

State chief minister Nitish Kumar has announced compensation of 200,000 rupees ($A3670) for bereaved families.

Free lunches are offered to impoverished students in state-run schools as part of government welfare measures in many of India's 29 states.

Bihar is one of the country's poorest and most densely-populated states.